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Trace Gemini CLI sessions, agent steps, model calls, and tool invocations in Phoenix for full observability.
Trace your Gemini CLI sessions in Phoenix with the coding-harness-tracing toolkit — every turn shows up as a trace with the model call, each tool it runs, and token usage, grouped into its session. No application code changes required: the toolkit hooks into Gemini CLI’s lifecycle events and streams OpenInference spans to Phoenix.

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Launch Phoenix

The fastest way to get started with Phoenix is by signing up for a free Phoenix Cloud account. If you prefer, you can also run Phoenix in a notebook, self-host it, or use it directly from your terminal. Go to the settings page in your Phoenix instance to find your endpoint and API key. A self-hosted Phoenix defaults to http://localhost:6006; the API key is only required when auth is enabled.

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Install

The curl installer is the simplest — it runs a short wizard that saves your Phoenix credentials for you. Use a local clone if you’d rather run the installer from a checkout of the source. macOS / Linux:
Windows (PowerShell):

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Local clone

The installer prompts for your backend — select Phoenix, then enter your endpoint and optional API key — and your project name, writes them to ~/.arize/harness/config.json, and registers the hooks in ~/.gemini/settings.json.

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Configuration

Credentials live in ~/.arize/harness/config.json. Environment variables override values in config.json and can be set in your shell profile.
On the Phoenix backend, set the project name with PHOENIX_PROJECT (or PHOENIX_PROJECT_NAME); ARIZE_PROJECT_NAME is Arize-only and ignored here. ARIZE_TRACE_ENABLED is a backend-agnostic harness setting and keeps the ARIZE_ prefix regardless of destination.

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Redaction controls

Each ARIZE_LOG_* flag accepts "true" or "false" and defaults to "true". Set to "false" to opt out per category:

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Observe

Once tracing is enabled, Gemini CLI activity is streamed to Phoenix. You’ll see:
  • Turn traces — each agent turn as a Turn (CHAIN) span, with the prompt as input and the final response as output
  • LLM spans — one LLM: <model> span per model call, with model name and token counts
  • Tool spans — one per tool call (read_file, run_shell_command, and others), with input, output, and duration
  • Session grouping — all turns from the same session grouped by session_id

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Reference

For the full list of environment variables, default file paths, and troubleshooting steps, see the Gemini tracing README.

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Uninstall

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Resources

Arize Coding Harness Tracing

OpenInference

Gemini CLI